Device for sealing closure clips

ABSTRACT

Method and device for sealing closure clips between a stamp and a bottom tool, wherein the sealing distance between stamp and bottom tool is monitored by a sensor.

This invention relates to a method of setting up a machine for sealingclosure clips between a stamp and a bottom tool, which for sealing theclip are first of all moved towards each other up to an adjustablesealing distance and are then moved away from each other. The inventionalso relates to a device for sealing closure clips between a stamp and abottom tool.

BACKGROUND OF THE INVENTION

One application for methods as stated above and the corresponding deviceis the sealing of bag-shaped or tubular packages, such as for instancesausages. These are frequently sealed with U-shaped closure clips madeof aluminum. High demands are made on the quality of such closure. Itshould not be so tight that the packaging casing is damaged when sealingthe same. At the same time, however, the closure should be sufficientlytight, and during processing steps subsequent to the sealing of asausage should not slip off the same. Due to these high demands made onthe closure, the extent to which the clip is compressed upon completionof the sealing operation--subsequently referred to as clip height--mustprecisely be achieved for the respective type of package by adjusting acorresponding sealing distance. This is first of all effectedempirically. Once the corresponding parameters for a type of producthave been defined, they can be adjusted on the sealing machine. In thecommercially available sealing machines it is generally possible toadjust the desired sealing distance. In most cases, a scale is provided,which provides for adjusting the same value for the clip height at alater date. Such sealing machine in the form of a desk top unit is knownfrom DE-GM 19 33 066.

When the sealing machine has been adjusted to the corresponding product,the sealing operation is performed as follows:

First of all, a portion of a tubular casing is filled with thefilling--for instance sausage meat. Subsequently, the filled sausagecasing is pinched by two pairs of displacement shears. The same willthen move away from each other axially with respect to the axis of thesausage and thus form a casing neck free from meat, which is disposedbetween the stamp and the bottom tool of the sealing machine. In thebottom tool, an open closure clip has been inserted. For sealing theclosure clip, stamp and bottom tool are moved towards each other, sothat the casing neck free from meat is seized by the open closure clip.Subsequently, the stamp impinges on the free legs of the U-shapedclosure clip, bending the same about the casing neck. For sealing thecasing neck, stamp and bottom tool first of all move towards each other,where they seal the closure clip and subsequently move away from eachother, in order to release the closure clip. At the turning point oftheir movement, stamp and bottom tool have a sealing distance from eachother which is decisive for the resulting clip height. The clip heightof a sealed closure clip thus results from the actual sealing distanceof stamp and bottom tool at the turning point between their movementstowards each other and away from each other.

Since the system of levers moving stamp and bottom tool applies forcesup to 2000 kg during the sealing operation, there will necessarily occura certain wear. The resulting clearance is not considered when settingthe sealing distance by means of the scale on the sealing machine. Theconsequence is that the scale reading does not correspond with theactual sealing distance and accordingly not with the actually resultingclip height either. Thus, the actually resulting clip height is not theoriginally determined desired clip height for which the sealing distancehas been adjusted on the scale. Even during a current production, thewear caused by the clearance of the system of levers leads to the factthat the sealing distance of stamp and bottom tool is constantlyincreasing, so that the closure clips are sealed less and less tight andfor instance during the subsequent processing of a sausage may slip offthe same.

Accordingly, the users of such sealing machines are forced nowadays tonewly check and possibly correct the tightness of the closure with eachproduction start. However, the testing methods are quite specific anddepend on the tester and thus are very subjective. The closure clipheight very frequently lies below the required height for safetyreasons, i.e. the closure clips are sealed too tight. As a result, thesealing machine is subjected to a much higher mechanical load than wouldactually be necessary, which leads to an increased wear and thus anearly failure of the machine.

SUMMARY OF THE INVENTION

It is the object of the invention to be able to monitor the sealingdistance independent of subjective influences. This object is solved bya method as stated above, where the sealing distance between stamp andbottom tool is detected by means of a sensor.

The gist of the invention consists in detecting the closure clip heightactually obtained in operation as a result of the wear of bearings, etc.In accordance with the invention this is advantageously effected bymeasuring the sealing distance between stamp and bottom tool. This isbased on the knowledge that the sealing distance between stamp andbottom tool is finally decisive for the quality of the closure. Byindirectly measuring the sealing distance, all influences determiningthe sealing distance are considered as well, whereas on the other handinfluences distorting the measurement result are avoided.

It is also conceivable to directly measure or change the sealingdistance, in that the maximum sealing force is detected by means of asensor, as is proposed by EP 0,467,020 A1. However, this variant has thedisadvantage that the measurement also includes the friction forcesoccurring upon sealing the clip and the deformation resistance of theclosure clip. The friction forces would be changed for instance by usinggreasy closure clips instead of dry ones.

A further advantage of the inventive method consists in that the sealingmachine can be switched off automatically when no or two closure clipsare present between stamp and bottom tool. In such cases, the requiredclip height is not achieved at all or exceeded with a correctly adjustedmachine.

What is preferred is a method where for determining the sealing distancethere is measured the distance between a distance sensor fixedlyallocated to the stamp or the bottom tool and a reference surfacefixedly allocated to the respective other part (bottom tool or stamp).This measurement is preferably effected in a contactless way, in orderto avoid a mechanical wear and an unnecessary formation of noise.

The sealing distance is readjusted when the measured sealing distancelies outside a range of desired values for the sealing distance. This ispreferably effected automatically. There is obtained a closed loop formonitoring the closure clip height during the operation, by means ofwhich expensive production losses due to incorrectly sealed packages orundesired interruptions for readjusting the closure clip height can beprevented.

The adjustment of the sealing distance between stamp and bottom tool isfor instance effected, as is known from DE-GM 19 33 066, by changing thegeometry of the stamp drive. This can particularly easily be effected inthat the sealing distance is adjusted by changing the length of alifting rod in the stamp drive.

The inventive solution of the object also consists in a device as statedabove, which includes a sensor for detecting a sealing distance betweenstamp and bottom tool as well as a means for adjusting the sealingdistance between stamp and bottom tool. With such a device it ispossible to determine the closure clip height while avoiding allpossible points of wear, and the user can thus benefit from alladvantages of the method in accordance with the invention.

In a preferred embodiment of the device the sensor is fixedly mountedwith respect to the bottom tool or the stamp and corresponds with areference surface fixedly mounted with respect to the respective otherpart (stamp or bottom tool).

The sensor preferably is a non-contact distance sensor. There is thusobtained a particularly simple construction hardly susceptible tofailure.

A preferred embodiment of the device includes a stamp drive, which has alongitudinally adjustable lifting rod. By means of this longitudinallyadjustable lifting rod the clip height can be adjusted. The lifting rodcan for instance be part of a lever mechanism which is driven by a camplate and together with the same forms the drive mechanism for stampand/or bottom tool. The line of movement of the stamp and/or the bottomtool can be predetermined by the shape of the cam plate.

The lifting rod is preferably equipped with a motor-driven actuator forthe rod length. The actuator provides for an automatic adjustment of therod length. When--as it is preferred--the distance sensor and theactuator are connected with each other by a control unit, there isobtained a closed loop for monitoring the clip height.

The invention and its variants will now be explained with reference tothe drawings and examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a simplified sealing system of a sausage sealingmachine,

FIG. 2 represents an embodiment with closed sealing tool and a sensorfor scanning the height of the closure clip in an enlarged segment ofthe sealing system in accordance with FIG. 1,

FIG. 3 represents the embodiment of FIG. 1 further comprising amotor-driven actuator, and

FIG. 4 represents the embodiment of FIG. 2 further comprising amotor-driven actuator.

DETAILED DESCRIPTION

The sealing system 10 of a sealing machine includes an upper sealinglever 12 and a lower sealing lever 14. Both sealing levers can beswivelled about a common pivot 16. The swivel movement of the sealinglevers 12 and 14 is effected by a not represented cam plate andtransmitted onto the same via lifting rods 18 and 20, which act uponpivots 22 and 24 at the sealing levers 12, 14. At the upper sealinglever 12 a stamp 26 is attached, and at the lower sealing lever 14 abottom tool 28 is attached. Into the bottom tool 28 an open closure clip30 has been inserted. Between the stamp 26 and the bottom tool 28 withthe open closure clip 30 there is disposed a casing neck 32 to besealed.

For sealing the same, the stamp 26 and the bottom tool 28 are movedtowards each other by a corresponding swivel movement of the sealinglevers 12 and 14, so that the casing neck 32 is seized by the openclosure clip 30. Subsequently, the stamp impinges on the free legs ofthe U-shaped closure clip and bends the same about the casing neck 32.Upon sealing the closure clip 30, stamp 26 and bottom tool 28 are againmoved away from each other, in order to release the casing neck 32sealed with the closure clip. At the turning point of their movement,stamp 26 and bottom tool 28 have the smallest distance from each other,at which the closure clip has been fully compressed to the desired clipheight.

This condition is shown in FIG. 2. The stamp 26 and the bottom tool 28have a sealing distance from each other--designated with "X" in FIG. 2,which also corresponds to the clip height. The closure clip 30' has beendeformed such that its free legs 34' and 36' are in contact with eachother and safely enclose the casing neck 32. In addition, the closureclip 30' has been compressed to the desired clip height "X".

The clip height "X" is adjusted by changing the length of the liftingrod 18. For a repeated adjustment of the length of the lifting rod andthus of the clip height "X" to a certain value, a scale is provided onthe sealing machine which is not represented in the Figures. Whenadjusting the clip height "X" by means of this scale, the clearancenecessarily occurring for instance in the pivots 22 and 24 and in thepivot 16 is necessarily disregarded. To be able to nevertheless performan exact adjustment of the clip height, a distance sensor 40 is fixedlymounted on the upper pivoted lever 12 with respect to the stamp 26. Thisdistance sensor makes a contactless measurement of the distance from areference surface 42 at the lower pivoted lever 14. The referencesurface 42 is fixedly mounted with respect to the bottom tool 28. Thereference surface 42 is part of a damping plate 46, which protrudes intothe space covered by the sensor 40 such that the same provides distancevalues with a maximum possible accuracy. The shape of the damping plate46 has been chosen accordingly. In the case of non-contact sensors,which respond to approaching metal particles, the damping plate 46 ispreferably made of metal.

Instead of the sensor assembly described above and represented in thedrawing, the sealing system might also include a force sensor fordetecting the sealing force, as the same is increasing with decreasingclip height "X". However, the sealing force does not exclusively dependon the clip height "X", but for instance also on the sliding anddeformation properties of the closure clip. With an otherwise identicaltype of closure clip, these properties in turn depend on whether theclosure clips are dry or greasy for whatever reasons, so that themeasurement of the sealing force does not allow an unambiguousconclusion as regards the clip height. Measuring the sealing distancebetween stamp 26 and bottom tool 28 therefore appears to be moreappropriate for determining the actual closure clip height "X".Nevertheless, a sensor for detecting the sealing force may be providedin addition, in order to differentiate for instance between deviationsof the actual clip height from the desired clip height, which are causedby the wear in the joints of the drive mechanism, and those resultingfrom the fact that possibly no closure clip 30 or even two of them havebeen inserted in the bottom tool 28.

Instead of the non-contact distance sensor described above andrepresented in the drawing, there may also be employed a hydraulicallyoperating distance sensor. In this case, a cylinder is mounted at theupper sealing lever 12, in which cylinder there is disposed a pistonwith a piston rod which protrudes from the cylinder and by means of areference surface at the lower sealing lever 14 can be pressed into thecylinder. The cylinder space above the piston is filled with a liquid,which is urged into a measuring tube when the piston rod is pressed intothe cylinder. The measuring tube is provided with a scale indicating theclip height. Such a hydraulic measurement system, however, has thedisadvantage that the zero point for the measurement is changed by theexpansion of the liquid column and must therefore newly be adjustedbefore each measurement. Moreover, the levers move towards each otherduring the sealing operation with a speed of about 2 m/sec, so thatdamages or disturbing noise may occur when the same hit a measuringinstrument. Therefore, the above-described contactless measurementsystem is preferred.

The sealing system 10 represented in FIGS. 1 and 2 can also be completedsuch that the lifting rod 18 is equipped with a motor-driven actuator 50(FIGS. 3 and 4). This actuator is operated by a control unit, in whichthe values for the actual clip height "X" determined by the sensor 40are compared with desired values. By means of the control unit and theactuator, the clip height "X" can automatically be readjusted in thecase of deviations from the standard. This control system can becompleted by the above-described force sensor for detecting the sealingforce. In any case, a sealing system is obtained, by means of which ahigh closure quality is achieved with little susceptibility to failure.

What is claimed is:
 1. A device for sealing closure clips, comprising abottom tool for holding said closure clips, a stamp, an upper sealinglever (12), a lower sealing lever (14) which sealing levers areswivelled about a common pivot (16), lifting rods (18, 20) attached tosaid sealing levers, said bottom tool being attached to said lowersealing lever, said stamp (26) being attached to said upper sealinglever, an adjustable and reversible actuator being connected to andacting upon one or both of said lifting rods for moving either of saidbottom tool or said stamp towards or away from the other, a sensor fordetermining a distance between said bottom tool and said stamp, and acontrol unit connected to said sensor and said actuator whereby inoperation said control unit automatically adjusts the operation of saidactuator in accordance with the distance between said bottom tool andsaid stamp determined by said sensor to maintain said distance at apredetermined value.
 2. The device of claim 1, wherein said distancesensor is fixedly attached to one of either the stamp or the bottomtool, and a reference surface is attached to the other of said stamp orbottom tool; and the sensor measures the distance between itself andsaid reference surface.
 3. The device of claim 2, wherein said sensor isa non-contact sensor.
 4. The device of claim 1, wherein said actuator ismotor-driven.